In recent years, as a method for manufacturing an SOI wafer, a method for manufacturing an SOI wafer by bonding an ion-implanted bond wafer and then delaminating the same (an ion implantation delamination method: a technology that is also called a smart cut method (a registered trademark)) has newly begun to attract attention. This ion implantation delamination method is a technology for, e.g., forming an oxide film (an insulator film) on at least one of two wafers, implanting gas ions such as hydrogen ions or rare gas ions from an upper surface of one silicon wafer (a bond wafer), forming a micro bubble layer (a sealed layer) in the wafer, then adhering the ion implanted surface to the other silicon wafer (a base wafer) through the oxide film, subsequently applying a heat treatment (a delamination heat treatment) to delaminate one wafer (the bond wafer) into a thin film form with the use of the micro bubble layer as a cleavage surface, and further applying a heat treatment (a bonding heat treatment) to achieve firm bonding, thereby providing an SOI wafer (see Patent Literature 1). According to this method, the cleavage surface (a delamination surface) is an excellent mirror surface, and the SOI wafer having high film thickness uniformity of an SOI layer can be relatively easily obtained.
However, in case of fabricating an SOI wafer based on the ion implantation delamination method, a damage layer formed due to the ion implantation is present on a surface of the SOI wafer after the delamination, and surface roughness is considerable as compared with a mirror surface of a regular product level silicon wafer. Therefore, according to the ion implantation delamination method, it is necessary to remove such a damage layer and the surface roughness.
In the prior art, to remove this damage layer and others, mirror polishing (a stock removal: approximately 100 nm) with a very small stock removal that is called touch polishing is carried out in a final process after the bonding heat treatment.
However, when polishing including a machining element is performed with respect to the SOI layer, since the stock removal of the polishing is not uniform, there occurs a problem that film thickness uniformity of the SOI layer achieved by implantation and delamination of hydrogen ions and others is deteriorated.
As a method for solving such a problem, there has been carried a flattening treatment for performing a high-temperature heat treatment in place of the touch polishing to improve surface roughness.
For example, Patent Literature 2 suggests adding a heat treatment (a rapid heating/rapid cooling heat treatment (an PTA treatment)) in a reducing atmosphere containing hydrogen without polishing a surface of an SOI layer after a delamination heat treatment (or a bonding heat treatment). Further, Patent Literature 3 suggests forming an oxide film on an SOI layer by a heat treatment in an oxidizing atmosphere after the delamination heat treatment (or the bonding heat treatment), then removing the oxide film, and subsequently adding a heat treatment (the rapid heating/rapid cooling heat treatment (the RTA treatment)) in a reducing atmosphere.
Furthermore, in Patent Literature 4, a sacrificial oxidation treatment is performed with respect to a delaminated SOI wafer after a flattening heat treatment in an inert gas, a hydrogen gas, or a mixed gas atmosphere containing these gases, whereby flattening of a cleavage surface and avoidance of OSFs can be achieved at the same time.
As described above, since the high-temperature heat treatment is carried out in place of the touch polishing and the flattening treatment for improving the surface roughness is effected, SOI wafers each having a diameter of 300 mm and excellent film thickness uniformity that a film thickness Range (a value obtained by subtracting a minimum value from a maximum value in a radial direction) of each SOI layer is within 3 nm can be obtained in a high-volume production level by the ion implantation delamination method.